Annealing furnace



Patented Dec. 5, 1933 UNITED STATES ANNEALIN G FURNACE Nelson Webb,-Belleville, N. 1., alslgnor to Eastwood-Nealley Corporation, Belleville,N. 1., a oom f tion of New Jersey App ication May 4,1931. Serial a...salsa": 12 Claims. (01. 200-4) This invention relates to electricfurnaces and the method of operating the same.

In the art of annealing material, particularly wire, it is extremelyimportant, especially where the wire isto be again drawn afterannealing, that the surface of the wire be substantially free fromoxides. Heretofore, great difllculty was encountered in this connection,for the oxides on the surface of the wire being extremely abrasive m incharacter, the wire could not be redrawn without seriously wearing thedrawing dies and requiring frequent substitution thereof. In annealingother materials, it is'also important, for one reason or another, toprevent oxides from forming on the surface of the material.

An object of the present invention is to provide an electric furnace andapparatus therefor where,- by oxidization is reduced to a minimumheretofore unobtainable. This is accomplished by closely controlling thecomposition of a non-oxidizing atmosphere within the furnace bypreventing atmospheric air from entering the furnace and therebycontaminating non-oxidizing atmosphere within the furnace, and byspeeding up the time required for cooling the annealed material andtherebyreducingthe time available for oxides to furnace embodying thisinvention and showing form on the surface of thematerial.

,Heretofore, it was suggested to heat the contents within the furnace byradiation alone or by radiation and convection of the heat developed bya resistance element or the like, but in such cases the amount of heatapplied to various parts of the material under treatment would not beequal, with the result that those parts in closer proximity tothe'source of heat would be brought to heat sooner than other parts,would get hotter, and would remain at the desired temperature longerthan other parts, resulting in an unevenness of treatment.

This difllculty is avoided, according to the present invention, byheating the material solely by convection and causing the atmospherewithin the furnace to circulate through the material being treated. Whenthe material being treated is wire, especially fine wire, this heatedcirculating atmosphere passes in and out between the strands of wire andheats the same substantially uniformly, and hence all parts of the sameroll or bundle of wire will receive the same treatment and accordinglywill have a more uniform tensile strength and constant modulus ofelasticity throughout'its l nd- This is accomplished in the form of theinvention shown herein, by encircling, the heating elements of thefurnace so as to shield the material being treated against receivingheat from the resistance elements, by radiation, and this mieldpreferablyforms a stack or chimney in which the atmosphere within thefurnace circulates and becomes heated in its circulation and from whichso it is directed over the material being treated. In order to increasethe speed of circulation where this is desirable,the present inventionprovides a blower or impeller, the outlet side of which is connected toa point within-the stack containing as the heating elements and theinlet side of which is located below the material being treated.

In order to facilitate the rapid cooling and hence decrease theopportunity for oxidization during the cooling operation, the presentinvention provides means for circulating the atmosphere of the furnacethrough a cooling medium, in addition to permitting the retaining wallto be removed without permitting atmospheric air to reach the interiorof the furnace.

Other features and advantages will hereinafter appear.

In 'the accompanying drawing showing one form of this invention, that atpresent preferred Figure 1 is a vertical section of an annealing themeans for controlling the atmosphere within the furnace.

Fig. 2 is ahorizontal section of the furnace taken on the line 2-2 Fig.1.

Referring more particularly to the drawing. the furnace embodying myinvention comprises preferably a cylindrical metallic shell 10 adaptedto match a base 11. As shown, the shell has a horizontal flange 12provided with annular Y-shaped ridges 13 adapted to fit similar ridges14 on the base 11. .An annular plate 15 is adapted to be piacedover theflange 12 and is bolted down to the base 11 by bolts 16 after a gasket1'7 is interposed between the annular flange 12 and the base 11, so asto make the connection between the shell and the base gas-tight. Theshell is preferably surrounded by a cylindrical furnace casing 18 ofsuitable refractory and heat insulating material so that during theapplication of heat to the material being annealed the loss of heat isavoided.

The heating elements 19 may be of any desired type or kind andpreferably are elongated so as to extend substantially the full heightof the chamber within the container or shell 10. The heating elementsare secured at their lower ends on an inverted cup 20 fitted within atube 21 pass ing through a hole in the base 11 of the furnace. This tube21 is preferably welded to the base so 110 as to form a gas-tightconnection, and, further, the inverted cup 20 supporting the heatingelements 19 is preferably welded to the tube 21 for the same purpose.The glowbars are secured to the inverted cup 20 by bolts 22 which areinsulated from the cup 20 and separately connected to curv rent supplywires 23.

The tube 21 is centrally located in the furnace chamber 24 within theshell 10 and, according to the present invention, has its upper end 25extending close to the top 26 of the shell 10 so as to completelyencircle and enclose the glowbars 19 and prevent radiation of the heatfrom the glowbars directly to the material under treatment in thefurnace chamber 24. The base 11 of the furnace is provided with agrating 2'7 of suitable grill work so as to form a support for thematerial above the base 11 and, at a point between the grating 27 andthe base 11, the tube is provided with apertures 28.

Hence, when the resistance elements 19 generate heat, the atmospherewithin the tube 21 is heated and rises, passing out of the open end 25of the tube and down around the outside of the tube 21 over and betweenthe material supported on the grating 27, thence down into the chamber29 under the grating 27 and through the holes 28 into the tube 21 backup through the tube where it is again heated by the resistance elements19. In this way, the tube 21, which, if desired, may be made ofrefractory materialyconstitutes a stack or chimney in which theatmosphere in the furnace is heated and rises. To facilitate thedistribution of the stream of gas rising within the tube 21 to all partsof the chamber 24, the top 26 of the shell 10 may be provided with adeflector 30.

For some purposes, it is sufllcient to depend upon this circulation ofthe atmosphere within the furnace. However, in other cases where it isdesired to more quickly bring the material being treated up to heat, thepresent invention provides means for artificially circulating theatmosphere through the furnace.

In the form of the invention herein shown, for accomplishing this thereis provided a blower or impeller 31 which may be driven by a motor 32.The inlet 33 of the blower 31 is connected as shown by a pipe 34, 35,36, multiple connection 37 and pipes 38 to pipes 39 which pass throughthe base 11 of the furnace and are preferably welded thereto. Thesepipes 39 accordingly will draw in the gas forming the atmosphere of thechamber 29 under the grating 27. The outlet 40 of the pump 31 isconnected by a pipe 41 to a pipe .42 which passes upwardly through theinverted cup 20 carrying the heating elements 19 and has its upper enddisposed within the tube 21 above the level of the holes 28. Hence, whenthe motor is operated and certain valves hereinafter referred to areopened, the atmosphere within the chamber 24 of the furnace is caused tocirculate, the stream of gas rising through the tube 21 and descendingon the outside of the tube and over the work passing through the piping34 to 39 inclusive above described, blower 31, and out through the pipe42 into the interior of the tube 21 and into contact with the heatingelements 19, thus augmenting the natural circulation resulting from theuse of the tube 21.

Heretofore, when the work had been brought up to heat and theremaintained for a desired given length of time, it was customary to allowthe work to naturally cool off. This in some cases was assisted by theremoval of the furnace casing 18,

and in the form of the invention shown herein, this is also providedfor, the casing 18 having an eye 43 by means of which it may be liftedand set aside while the container or shell 10 is allowed to remain onthe base 11.

Notwithstanding the fact that the removal of the furnace casing allowedthe container to cool off more rapidly, the operation of cooling off thework required a relatively long time, thus keeping the furnace idle andunproductive for heating purposes and allowing more time for any freeoxygen in the atmosphere of the chamber 24 to collect and form a coatingon the work.

Accordingly, it is an object of this invention to further acceleratecooling of the work to a temperature at which it' may be removed fromthe furnace without danger of becoming oxidized.

To this end, the present inventionprovides a gas cooling device 44through which the gas forming the atmosphere of the furnace may beshunted in the course of its being drawn from and blown into thecontainer 10 by the blower 31.

In the form herein shown, which is more or less diagrammatic, thecooling device includes a coiled pipe 45 connected to the pipe 35leading to the pipes 39 through which the gas is drawn from the chamber29 under the work. At its other end it is connected to an inlet 33 ofthe blower 31. The cooling pipe 45 may be brought in contact with anycooling medium, but, as shown, it is contained in a tank 46 having awater inlet 4''! and an outlet 48.

After the WCIk has been annealed and it is desired to rapidly cool thesame, a valve 49 in the pipe 34 is closed and valves 50 and 51connecting the pipe 35 and inlet 33 respectively with the cooling coil45 are opened, thus causing the gases forming the atmosphere of thecontainer 10 to be drawn through the cooling pipe 45 by'the blower 31before it is blown into the interior 'of the tube 21'by the outlet pipe42.-

In heating the material, the hot non-oxidizing gases escaping from theopening 25 of the tube 21 and passing down through the work toheat thelatter by convection naturally brings the upper parts of the work toheat more rapidly than the lower parts due to the heat absorbed as thegas descends and hence the upper part of the work is brought to heatsooner than'the lower part of the work.

Since the heating is by convection, and therefore gradual, this is inmany cases unobjectionable. However, according to the present invention,this inequality in heating is overcome by causing the gases cooled bythe cooling device 44 to flow in the same direction as the heated gaseswith the result that the upper part of the work is cooled sooner thanthe lower part'of the work, and accordinglyyby regulating the rate ofcooling so as to equal the rate of heating, all parts of the work may becaused to receive the same quantity of heat for the same length of time.

In annealing'materials in such a way as to prevent oxidization, it isessential that the purity of the non-oxidized gas be maintained at ahigh 1 standard and for this purpose the present invention providesmeans for feeding a supply of fresh non-oxidizing gas to the container10 and the circulating system while thelatter is in operation, or inpreparation for the operation of the has connected to it a pipe 54leading to a tank or reservoir 55 of non-oxidizing gas, the e from whichis controlled bya valve 58.

In preparing for the annealing operationafter the work has been placedon the grate 27 and the container 10 has been clamped in place on thebase 11 with the casing 18 surrounding the container and with all of thevalves in the system, excepting the gas tank valve 56, open, the latteris opened to allow the non-oxidizing gas to flow into the container andthrough the regulating system expellingthe atmospheric air through theoutlet pipe 52 which, being at the lowest point in the system, permitsthe heavier atmospheric air to be expelled through the valve 53. At thistime the blower 31 is operated for a short time to clear it of anyatmospheric air that may be trapped therein. 1 When the atmospherewithin the casing 10 and circulating system is clear of atmospheric air,the valves 53 and 56 are closed. At the same time, the valves 50 and 51leading to and from the cooling device 44 are closed and the current isturned on so as to cause the heating elements 19 to operate.

If the circulation of the gas within the fumace is in this particularcase a natural circulation resulting from heating of the gas in the tube21 and the cooling of it outside the tube 21, the valve 49 is closed soas to prevent circulation of the gases through the circulating system.If, however, the circulation is to be artificially augmented, the valve49 is opened and the blowercaused to operate. After the work has beenheated to the desired degree, the circuit through the heating elements19 is broken, the valve 49 closed, and the valves 50 and5l opened, soas-to cause the gases to be circulated through the cooling de vice, 44.

Thus it will be seen that the furnace of the present invention providesvery. efllcient means for obtaining a uniform heat on articles which areto be annealed, provides means for maintaining the atmosphere within thefurnace free from oxidizing gases, also provides means for acceleratingthe work heating or the cooling operation, and particularly providesmeans to reduce very undesirable work oxidization to a minimum. 7

In its broader aspects, the invention is not to be limited to annealing,although its greatest application or use will no doubt be for thispurpose; but, it should be understood that the present invention may beused, for example, to harden mushet steel,'which is accomplished withoutimmersion in an oil or water coolant, but is accomplished in practicallythe same manner as an annealing operation, for most other materials.Similarly, the furnace of the present invention may 'beusedadvantageously to variously heat treat divers materials in controlledatmospheres.

Variations and modifications may be made within the scope of thisinvention and portions of the improvements may be usedwithout others.

Having thus' described the invention, what is claimed as new and forwhich it is desired to obtain Letters Patent, is,

1. In an annealing furnace, the combination of a gas-tight container andan electrical resistor supported therein substantially centrallythereof, of means for supporting work to be heated in the space be'-ween the resistor and the walls of the container; and means interposedbetween the work and the resistor and surrounding the latter to preventthe work being heated by radiation.

2. In an annealing furnace, the combination of a gas-tight container andan electrical resistor supported therein substantially centrallythereof, of means for supporting work to be heated in the space betweenthe resistor and the walls of the container; and means interposedbetween the work and the resistor and surrounding the latter to preventthe work being heated by radiation, said means having openings at thetop and bottom and causing the atmosphere within it and heated by theresistor to rise and escape through the upper opening to the spaceoccupied by the work, descending through the work to heat the latter andreenter said means through the lower opening to be again heated by theresistor.

3. In an annealing furnace, the combination of a gas-tight container andan electrical resistor supported therein substantially centrallythereof, of means for supporting work to be heated in the space betweenthe resistor and the'walls of the container; and means interposedbetween the work and the resistor and surrounding the latter to preventthe work being heated by radiation, said means comprising a stack havingupper and lower openings through which theatmosphere of the furnace maycirculate to be heated and reheated.

4. In an annealing, furnace, the combination of' a gas-tight containerand an electrical resistor supported therein substantially centrallythereof, of means for supporting work to be heated in the space betweenthe resistor and the walls of the container; means interposed betweenthe work and the resistor and surrounding the latter to prevent the workbeing heated by radiation, said means comprising a stack having upperand lower openings through which the atmosphere of the furnace maycirculate to be heated and reheated; and means including a conduitleading from, the exterior of the container and entering the stack abovethe lower opening for cooling the atmosphere to be circulated upwardlythrough the stack and downwardly through the work after the heatingoperation has been completed.

5. In an annealing furnace, the combination of a gas-tight container andan electrical resistor supported therein substantially centrallythereof, of means for supporting work to be heated in the space betweenthe resistor and the walls of the container; means interposed betweenthe work and the resistor and surrounding the latter to prevent the workbeing heated by radiation, a blower, and conduits leading from thecontainer to'the blower and from the blower back to the container forcausing the atmosphere to be circulated in the container over theresistor and through the work to be heated.

6. In an annealing furnace, the combination of a gas-tight container andan electrical resistor supported therein substantially centrallythereof, o

mosphere to be circulated in the container upwardly over the resistorand downwardly through the work to be heated.

7. In an annealing furnace, the combination of a gas-tight container andan electrical resistor supported therein substantially centrallythereof, 5o

of means for supporting work to be heated in the space between theresistor and the walls of the container; a tube interposed between thework and the resistor and surrounding the latter to prevent the workbeing heated by radiation, said tube having an opening at the top;alblower; and conduits leading from the container and from the blowerback to the container and opening into the interior of the tube forcausing the atmosphere to be circulated in the container up-p wardlyover the resistor and downwardly through the work to be heated, saidconduit leading from the container to the blower having an inlet openingunder the work and in the space outside said tube.

by the work, descending through the work to heat the latter and reentersaidmeans through the lower opening to be again heated by the resistorby natural circulatiomand means including a blower and a conduit leadingfrom the bottom of the space in whichthe work is adapted to be supportedto the blower and a conduit from the blower to the container openinginto the interior of said means surrounding the resistor to augmentnatural circulation of atmosphere in the container past the resistor andthrough the work. i

9. In anannealing furnace, the combination of a gas-tight container andan electrical resistor supported therein substantially centrallythereof, of means for supporting work to be heated in the space betweenthe resistor and the walls of the container; means interposed betweenthe work and the resistor and surrounding the latter to prevent the workbeing heated by radiation, said means having openings at the top andbottom and causing the atmosphere within it and heated by the resistorto rise and escape through the upper opening to the space occu-' pied bythe work, descending through the work to heat the latter and reentersaid means through the lower opening to be again heated by the resistorby naturalcirculation; means including a blower and a conduit leadingfrom the bottom of the space in which the work is adapted to besupported to the blower and a conduit from the blower to the containeropening into the interior of said means surrounding the resistor toaugment natural circulation of atmosphere in the container past theresistor and through the work;

a cooling device; and means for shunting the atmosphere impelled by theblower through the cooling device before it again enters the containerto accelerate cooling of the work after the latter has been heated. r

10. In an annealing furnace, the combination of agas-tight container andan electrical resistor supported therein substantially centrallythereof,nof means for supporting work to be heated in the space betweenthe resistor and the walls of the: container; means interposed betweenthe work andthe resistor and surrounding the latter to prevent the workbeing heated by radiation, said means having openings at the top andbottom and causing the atmosphere within it and heated by the resistorto rise and escape'through the upper opening to the space occupied bythe work,-descending through the work to heat the latter and reentersaid means throughthe lower opening to be again heated by the resistorby natural circulation; means including a blower,

and a conduit leading from the bottom of the space in which the work isadapted to be supported to the blower and a conduit from the blower tothe container opening into the interior of said means surrounding theresistor to augment natural circulation of atmosphere in-the co'ntainerpast the resistor and throughthe work; and

means for supplying fresh gas to the container through said conduits.

11. In an annealing furnace, the combination of a gas-tight containerand an electrical resistor supported therein substantially centrallythereof, of means for supporting work to be heated in the space betweenthe resistor and the walls of 1 5 the container; means interposedbetween the work and the resistor and surrounding the latter to preventthe work being heated by radiation, said means having openings at thetop and-bottom and causing the atmosphere within it and heated by theresistor to rise and escape through the upper opening to the spaceoccupied by the work, descending through the work to heat the latter andreenter said means through the lower opening to be again heated by theresistor by natural circulation; means including a blower and a conduitleading from the bottom of the space in which the work is adapted to besup ported to the blower and a conduit from the blower to the containeropening into the interior of said means surrounding the resistor toaugment natural circulation of atmosphere in the container past theresistor and through the work;

a cooling device; means for shunting the atmosphere impelled by theblower through the cool- 1, ing device before it again enters thecontainer to accelerate, cooling of the'work after the latter has beenheated; and means for supplying fresh gas to the container through saidconduits during the cooling process as the gas in the con- 1 tainertends to decrease in volume as it cools.

12. An annealing furnace having a gas-tight container; work-supportingmeans therein; heating elements therein; and a centrally disposed stackof relatively small displacement enclosing 111': said heating elementsfor positively forcing the atmosphere in the container to circulate overthe heating elements and through the work to be heated.

NELSON WEBB, I40

